Circulation pump drive and fuel shutoff control for forced circulation boilers



Jall- 25, 1955 D. M. scHoENFELD 2,700,353

CIRCULATION PUMP DRIVE AND FUEL SHUTOFF CONTROL FOR FORCED CIRCULATION BOILERS Filed Deo. 22. 1949 2 Sheets-Sheet l I I I 6/ I :l DP

l I f `T; 79 76" Diff. Pres/ 5 E 62 72 INvENToR Fig' L David M. Schoenfeld ATTO EY Jall- 25, 1955 D. M. scHoENFELD CIRCULATION PUMP DRIVE AND FUEL SHUTOF'F CONTROL ROR FORCED CIRCULATION BOILERs Flled Dec 22 1949 2 Sheets-Sheet 2 Feedwater INVENTOR A David M. Schoenfeld United States Patent M David M. Schoenfeld, Scarsdale, N. Y., assigner to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Application December 22, 1949, Serial No. 134,514

Claims. (Cl. 112-448) This invention relates to steam generators that are equipped with forced circulation pumps having both high 'capacity and low capacity driving means, and it has. special reference to activating such driving means in proper accordance with the steam loading on the generator and to protecting the generator from overheating should the pump-produced water circulation through the boiler tubes fall below the minimum called for by the steam loading on the generator.

Broadly stated the object of my invention is to accomplish the foregoing activation and protection automatically and in a simple yet highly reliable manner.

A more specific object is to provide improved means responsive to a measure of the steam load supplied by the generator for causing the circulation pump to be driven at low speed when said load is less than a given value and at high speed when the load exceeds that value.

Another object is to provide cooperating means that are effective to cut off the fuel supply to the boiler should the pump, when driven either at high speed or@ at low speed, fail to circulate water through the steam generating tubes at a rate adequate for the steam load being carried by the boiler.

Other objects and advantages of the invention will become apparent from the following description of illustrative embodiments thereof when taken in conjunction with the accompanying drawings wherein:

Fig. 1 is a diagrammatic representation of my new control system applied to a steam generator that is equipped with a forced circulation pump which has alow-speed driver in the form of a low capacity electric motor and a high-speed driver in the form of a higher capacity steam turbine; and Y a h Fig. 2 shows how the control and protective facilities of Fig. l may be applied to a forced circulation boiler whose pump is driven by a single electric motor which operates at low speed when energized over one connection and at high speed when energized over another connection.

The illustrative steam generator to be benefitted from the header through the generators combustionA chamber 17 and thence to the drum 10.

Boiler water is circulated by pump 14 Athrough .the

steam evaporation tubes 12 at'rates equal to several times the weight of steam that is evaporated inthe tubes'and discharged from drum 10 to steam outlet 18. If desired a check valve (not shown) may be interposed between,

pump 14 and header 15 for the purpose of assuring that water circulation can proceed only in the direction (as indicated by the arrows) of from pump 14 through tubes 12 to drum 10 and thence back .to the pump.

As here shown the evaporation tubes 12 are housed within walls 20 forming the aforesaid furnace chamber 17; at the upper portion of said chamber the tubesmay pass back and forth to form the illustrated convection bank; and within the furnace oltake 21 there may be located a superheater 22 leading from drum 10 to youtlet header 23 and thence to steam discharge conduit 18. As

tor at a other arrangements of generator pressure parts are both possible and common, it will be understood that the forced circulation organization here schematically disclosed is illustrative rather than restrictive.

Fuel for firing the represented steam generator may be introduced into combustion chamber 17 in any suitable manner as through the medium of one or more burners 25. Only one such burner 25 is here shown, and the form thereof has been sirnplied to facilitate explanation. 1t will be assumed that this burner 25 is designed to utilize fuel oil supplied thereto from a suitable source represented at 26; as the description proceeds it will become apparent that other burner designs (as oil recirculating) and other fuels (as gas or coal) also are useable inthe boilers to which my invention is applicable.

Adjustment in the rate at which the represented burner 25 injects the burning fuel into furnace chamber 17 may be effected in any suitable manner as through the medium of an adjustorvalve 27. Setting of valve 27 to hold the generated steam pressure, as indicated at gage G, at a desired constant value may be accomplished either manu ally or automatically, as through the medium of conventional adjustor means indicated generally at 28.

Regardless of whether such adjustment is effected manually or automatically, high steam loadings on the generator will call for correspondingly high rates of fuel supply to burner 25 through valve 27; intermediate steam loadings on the generator will call for an intermediate setting of fuel adjustor valve 27; and low steam loadings will require that valve 27 be opened only the small amount needed to supply fuel burner 25 at a corresponding low rate. In other words a flow of fuel through the fuel supply pipe 26 and burner 25 is controlled in accordance with thel steam load on the generator 12 t0 maintain the desired boiler operating pressure; steam load being defined as the pounds of steam per hour consumed by steam utilizing apparatus and supplied by the genera- (for all practical purposes) constant pressure which may be either the designed pressure of the boiler of some other predetermined pressure. When'the ad- Justment of valve 27 is effected automatically the conventional adjustor means 28 would of course take the form of an intricate modulator control device which would be effective to maintain the aforementioned constant pressure. This result is brought about by gage G responding to the pressure in header 23 by moving the indicator and other mechanism (not shown) either in the clockwise or counterclockwise direction in response to an increase or a decrease of pressure in said header 23 from its predetermined constant value which increase or decrease is brought about by a change in the load oii the generator. If the load increases the pressure'in header 23 initially falls while if the load decreases the pressure in said header initially rises. In response to the aforementioned moving of gage G adjustor 28 is effective to adjust va1ve'27 in such a manner as to regulate the fuel supplied to and accordingly the heat input of the boiler so as to restore the pressure in header 23 to the aforesaid constant value.

High-speed and low-speed driving means for circulation Pump The earlier described water circulation pump 14 for the steam generator is shown as receiving driving rotation through a shaft 31 and a 'gear wheel 32 carried thereby. Meshing with one side of this gear wheel isa first pinion 33 driven by a first prime mover which ytakes the form of a low capacity electric motor 34; and meshing with the other side of the same pump driver gear 32 is a second pinion 35 driven by a second prime mover which takes the form of a higher capacity steam turbine 36.

With this arrangement it is possible to drive circulation pump 14 either by electric motor 34 or by steam turbine 36. Overrunning clutches 37 and 38 may if desired be used in the motor and turbine output shafts so that whenl Patented Jan. 25, 1955v Clllion pump 14at. the high speed which must accompany high steam loadings on tho. generator... Motor. 3x4. on the other hand is oflower capacity and is adapted to drive circulation pump 14 at the low speed adequate when the steam generator is operating under low steam ndings. In` either eventthe driven pump 14j iuncti'ons t9. deliyer waterto header 15 at a pressure sufiiciently above boiler pressure (in'drum 10) to overcome the resistance. of the evaporation vtube circuits 12A (including orifices therein-not here shown) when pumping` the required weight of water corresponding to the steaming rate of the boiler. The weight of boiler water socirculatedthrough the tubes12 typically will be several times thatk of the steam being-evaporated in those tubes; this ratio varying with the installation.

'I=`o facilitate explanation, let it be assumed that the steam turbine 36 hasl a capacity of 100V horsepower and serves to drive circulation pump 144 at a speed' of' about 1500 R. P. M.; that electric motor 34 has a capacity of' 15 horsepowerfand serves to drive boiler pump 14 at a speediof approximately 500 R. P. M.; that the latter low speed (500 R. P. M.) of pump operation is adequatefor starting up the steam generator and for sustaining steam loadings thereon upto approximately and thatl the highturbine speed (1500 R. P. M.) of pump operation is called for only to sustain steam generator loadings in the range above 20% rated capacity.

Control of. motor and turbine. operation and l0ad. responsive selection therebetween In. the illustrative arrangement shown, steam for drivf ing turbine 36 is suppliedA thereto from conduit 1.8. of the steam generator throughpiping 40 which includes nor.- mally closed valve 41; current for driving motor 3 4 is supplied thereto from power circuit A-B-.C through normally opened'` switch contacts 42; the normally closed turbine valve 41 isV provided with a solenoid 44 which when energizedeiects an openingof the valve and therebyv admits driving steam tothe turbine 36; and the normally opened motor switchl is provided with a solenoid 45,. which when energized serves to close switch contacts 421andsupplyv driving current to motor 34. Deenergization of solenoid 44. isaccompanied by reclosure of turbine valve 41: and stoppage of turbine 36; and deenergization of solenoid 45 is accompanied by a reopening of motor switch 42 andl stoppage of motor 34 In accordance. with my invention I control theoperation, of motor 34 and of tur-bine 36 in response to a measure of the steam load supplied by the generator; this control being accomplished in a novel manner which causes the circulation pump 14 tobe driven at low speed by motor 34 when said load is less than a given value (earlier assumed to be 20% of rated generator capacity) and at high speed by the turbine 36 when thel steam vload exceeds that given value.

For accomplishing -such novel control automatically anysuitable measure of the steamloading on the genera tor may be utilized; a steam flow meter SF anda fuelflow meter FF here being shown to provide such required measure.

As here represented, steam ow meter SF is actuated bythe pressure.v drop across an orice 4'7 in the steam outputline 13; response to the. pressure drop across some other part of the supplied steam system, such as Vsuperhcatcr 2.2., is. of course also possible. for providing thcv measurement desired. VIn either event meter SF positions pointer 48 in accordance with the rate at which the generator is supplying steam through output4 line 18; pointer 4S .occupying the extreme left positionl shown under conditionsgof zero output, the extreme right position when theQgenerator output is maximum, and intermediate posi. tions;iorintermediatesteam loadings., They represented instrument SF further` includes a stationary4 Contact 49 which' isv disengaged from pointer 48- wheny the` generator steam load is within the range. below 20% full rated, and. which is engagedv by that4 pointer for all steam loadson` the generator ofy 20% rating or above.

Inl the illustrative form here shown, the fuel. dow-meter FEy issA actuated by the pressure drop across an orifice 51;Y inthe line 26 through which fuel is. supplied to burner 25,. This meter also isprovided with. a pointer 52 and a stationary contact 53. When the. burner is. receiving fuel at lo.w rates corresponding to less than. 20% steam loading on the generator pointer 52 is disengaged. from contactrS.; however when burner 25 receives fuel at rates corresponding to steam loadings of 20% rated and higher on. generator. than. oointor. 5.2., engages. Contact. 5.3.-.

Since the pressure in header 23 is maintained constant, as hereinbefore explained, it is apparent that the pressure drop across and accordingly the ow through orice 47 is responsive to and gives an indication of the previously defined steam load on the generator. It is further apparchi that since thc tuclfsupply tothogcncrator, i. c., the. ow of fuel through the4 fuel. supply conduit, isregul'ated -in accordance with 4said steam load, as previously explained, a device indicating the flow of fuel through said fuel supply conduit likewise gives an indication of the steam load on the generator.` Thus since both of the meters SF and FF are electively responsivev to thel steam load on the generator and accordingly give an indication of said steam'load either one of these instruments may be utilized to determine when the.I driyefor circulating pump 14 shall be transferred from low speed motor 34 to high speed turbine 3,6y and vice versa.

Any suitable` moans for causing. either stoamow mctcr SF or fuel. oyv motor. FFJ to, control thc functioning of. motor`- 3.4 and turbina. 36i11ihc, manner aforesaid may off course bc cmployod- Possibilities includa hydraulicy con.-

trol'` deyices, air operated,y control; facilities, Or, electrieal circuits and, dcyiccs.- In. thc. embodiment of: my ini/cnf.

tion. here disclosedy electrical facilities are utilized; but as.

the description proceeds it will become apparent that suclr utilization is illustrative rather than restrictiye and that hydraulic or air operated rncansmay bc substitutedwithout departingvfromfthe spirit and scope of my invenv. tion.

Forming a part of the electrical system represented is a source of control potential designatedby vertialcon: ductors 55 and: 56' respectively shown at the left and, at the right of Fig. l. Between these,p1ll and. minus conductors there is maintained; a suitable control potential such as 11.0 volts diretcurrent,

Also utilized' in the represented controll system,l for motor 34 and turbine 3 6 is a load relay LR. This relay is providedwitlra` lcoi'itactSS whichy occupies; the released.

(or lower) position shown as long as the relay winding (shown.k immediately above thc Lldcsignationl is dcenergized but which moves upwardly to the4 picked up position whenever the winding off relay LR is connected4 across supply conductors 5 5-.565

Control of such connection is accomplished by. thc steam flow meter SF when a selector switch59l is inthe upward position shown and, by the` fuel owmeter EF when switch 59 is moved, to the downward position.

tshle load relay LRunder the coniroly ofv steam flow meter From the diagram of Fig. l itY will be seen that asV long as a startingvswitcheilj has the open, position shown Thus. cncrsizcd solenoidA 4.5v closes switchv contacts. 42.

ihcroby connecting motor 3'4 lwith. energizing circuit. A-B'--C and placing. thc motor in. operation Since thcscncraior. is. Producingv no. s tcain pointer 4s of. ow

motor. Slliccps. load. relay, LR dconorsizod. solenoid 44. allows turbine-valve 41 tod remainl closed, and turbineV But motor 34, cnoraizcd as.

35.' S- illus kent.: inattivo, aferesaid,l new. drives circulation pumpl 14 at the slow speed ofy about 5,0QR. P.M;. This. causesthe pumpto. circulate water through the, steam. generating tubes. 12A` at a rate adequate for steam, loadings on the generator of up to aboutI 20%; full rated capacity.

The circulation thus having been. started, fuel valve 275 can hc. partially oncnsld andburncr 2,5. lighted to provide in combustion chamber 1 7 heat which generates;V

in tubes 12- steam that passes into drum lil'-V and', thence through superheater 2`2fY to outletconduit 18. Low capacity motor- 34 will now continue to operate either .until starting switch 60h is opened `oruntilfthe rate of In. thckr 'i description of control. system, opcration. now to follow it will-first be assumed` that switclr 59' is, up thereby placing Starting switch 60 is4 first thc. switch blade, 60. and@` fuel supply to burner 25 has been raised to a Vpoint where the steam loading on the generator rises to above the aforesaid 20% rated value.

When the latter happens, pointer 48 of ow meter SF will engage contact 49 and complete for load relay LR a pick up circuit extending from supply conductor 55 through conductor 63, the winding of relay LR, switch 59, engaged elements 48--49 of meter SF, and conductor 64 to supply conductor 56. Thus energized, relay LR moves contact 58 upwardly to its front point thereby disconnecting motor switch solenoid 45 from supply condutcor 56 and connecting turbine valve solenoid 44 therew1 By reason of said disconnection solenoid 45 allows switch contacts 42 to reopen and shut down the motor 34; said reopening preferably occuring after a short time delay provided in any suitable manner as by the represented condenser 66 bridged across winding 45 and serving to continue current ow therethrough for a short period following the pickup of load relay LR. In practice this delay period may be chosen to span the interval required by turbine 36 to come up to speed following the now initiated opening of steam supply valve 41.

Said steam valve opening is accomplished by solenoid 44 upon the aforesaid pickup of load relay LR; that solenoid then being energized over a circuit extending from supply conductor 55 through the winding 44, front contact 58 of picked up relay LR, closed starting switch 60, and conductor 62 to supply conductor 56. The thus energized solenoid 44 opens normally closed valve 41 and allows steam from the generator outlet header 23 to ow through piping 40 into the pump driving turbine 36. Thus activated the turbine now drives boiler circulating pump 14 at a high speed earlier assumed to be 1500 R. P. M.

When so driven by the high capacity turbine 36 the pump circulates water through steam generating tubes 12 at a rate adequate for loads up to full steam generating capacity of the boiler furnace. As long as this loading remains above 20% rated, ow meter SF keeps pointer 48 in engagement with contact 49, thereby holding load relay LR picked up and causing solenoid 44 to maintain turbine valve 41 open.

Assume next that the steam load on the generator drops to some lower value (as belowl20% rated) at which the high speed driving of pump 14 no longer is necessary. When the decrease has reached 20% of rated load, llow meter SF moves pointer 48 to the left away from contact 49. This breaks the pickup circuit of load relay LR and releases contact 58. l

Such release disconnects turbine valve solenoid 44 from control conductor 56 thereby allowing turbine valve 41 to reclose; at the same time the now released contact 58 reconnects motor switch solenoid 45 with said conductor 56. Accordingly as the high capacity turbine 36 is taken out of operation the low capacity motor 34 is started up, and circulation pump 14 is again driven at the slow speed earlier assumed to be 500 R. P. M.

Should it be desired to stop the circulation pump 14 completely this may be accomplished merely by opening starting switch 60. Such opening deenergizes solenoid 45 to cause an opening of switch contacts 42.and resultant shut down' of the motor pump 34; it likewise isolates turbine control solenoid 44 from energizing conductor 56 thereby making admission of steam to the turbine 36 impossible.

Load-responsive selection from fuel flow meter FF The foregoing operating sequence for low capacity motor 34 and high capacity turbine 36 is substantially duplicated when the control thereof is shifted from steam ow meter SF to fuel flow meter FF. As earlier indicated such shift is accomplished by moving transfer switch 59 to the downward position wherein the winding of load relay LR is connected with device FF through conductor 68. With this new set up the loading on the steam generator is measured by fuel meter FF the pointer and contact elements 52-53 of which now accomplish the same function as did pointer and contact elements l48-49 of steam ow meter SF.'

As long as the burner 25 is supplied with fuel from 1ine.26 at a rate corresponding to steam generator loadings below a given value (earlier assumed to be 20% rated) meter FF keeps pointer 52 disengaged from contact53. Hence, with starting switch 60 closed load relay LR stays released, motor switch solenoid 45 is energized over back contact 58, and contacts 42 connect supply circuit A-B-C with motor 34. This causes the low capacity motor 34 to drive boiler pump 14 at the slow speed (assumed to be 500 R. P. M.); high capacity turbine 36 being kept inactive under this condition.

When however the rate of fuel supplied to burner 25 rises to a value corresponding to steam generator loadings above 20% rated, fuel flow meter FF moves pointer 52 into engagement with contact 53. This picks up load relay LR over a circuit extending from supply conductor 55 through conductor 63 and winding of relay LR, transfer switch 59 in its downward position, conductor 68 contact and pointer 53-52 of device FF, and conductors 69 and 62 to supply conductor 56.' Load relay LR now again picks up (as before) breaking at back contact 58 the energizing circuit for motor switch solenoid 58 and completing at front contact 58 `the earlier traced energizing circuit for turbine valve solenoid 44.

In consequence the high capacity turbine 36 now replaces the low capacity motor 34 in driving circulation pump 14. By reason of its resultant operation at high speed (assumed to be 1500 R. P. M.) that pump now circulates water through steam generating tubes 12 at a rate adequate for the highest steam loadings of which the generator is capable.

Upon drop in the generator steam output the rate of fuel supply to burner- 25 drops accordingly and when the load has decreased to about 20% fuel meter FF moves pointer 52 to the left away from contact 53. This breaks the pick up 'circuit for load relay LR and by releasing contact 58 substitutes low capacity motor 34 for high capacity turbine 36 in driving the circulation pump 14.

As earlier indicated shutdown of the entire system may be effected merely by opening starting switch 60. Moreover, to reassign control of load relay LR back to steam ow meter SF (from fuel flow meter FF) it is only necessary to shift transfer switch 59 back into the upward position.

The just described automatic control of low capacity (motor 34) and high capacity (turbine 36) driving prime movers for circulation pump 14 assures important economies in the energy consumption required to drive that pump. vSteam generators of the forced circulation type here illustrated are sometimes operated for prolonged periods at relatively low steaming rates. Under such operating conditions the expenditure of horsepower (assumed for turbine 36) to drive circulation pump 14 represents a considerable wastage of energy over expenditure of only 15 horsepower (assumed for motor 34) which is entirely adequate to drive the pump as'long as the steam load stays within the lower range. The automatic control and transfer facilities just described are therefore instrumentalin'eifecting important savings in boiler operating cost.

Overheat protection of boiler by automatic fuel shutoff Steam generating boilers of the forced circulation type here disclosed require that a minimum rate of water circulatlon through evaporating tubes 12 be maintained during' operation otherwise those tubes may become seriously damaged due to overheating. The complete control system of my invention also provides protection against this' possibility.

ln the illustrative arrangement here disclosed, such pro tection is exercised through a shutoff valve 71 disposed' in thehfuel supply line 26`leading to burner 25. This valve 1s normally open and thus ordinarily allows free ow of the fuel to burner 25 in any quantity that may be determined by the setting of fuel adjustor valve 27.

In order that shutoff valve 71 may be closed -at proper thereacross is zero and the pointer 75 of instrument DP I then occupies the extreme left position shown. As the pump speed vbuilds up it creates between pump inlet 13 and pump outlet 15 a differential pressure which is roughly proportional to the speed at which the pump is rotated and4 whichserves to torce.v thewaterfrom .drumt 1D :throughthe. steam evaporatingv tubes: 12rv in. the. manner earlier: explained..

'log facilitate explanationit. will be. assumed: that adriw ing of pump 14-by low capacit-y motorY 34 at 5.00 R. P. M. produces a differential pressure or" about 5 lbs. per, square. in ch and that a ,driving of the. pumpbyfhighcapacity,y turbine ,36 yat4 15 00` R. P. M. .produces an elevated; differential pressure of the order of about: 3.5-lbs; per square'` inch.

Let itfurther be assumed that when the, steam-generator is. operating; inthe lowv capacityr range (earlier assumedl to be under of full rated) the steam; generating tubes 12? will not; beindanger of overheating as long as.- the pump 14drivenby motor 34.at about 500 R. P. M. conh titluesto hold, itsdifferential pressure above` 3 lbs. per square inch; and that. when.; the generator isA operating; at. loadllevelsof above 20% ratedand pump. 1.4 isbeing; drivenby turbine 36 at about. 1500 R. P. M; the aforesaidy generating tubes 12 will not besubjected to danger from; overheating as long as the pump produces a differential pressure of'above. 15 lbs; per square` inch;

On: the basis of the foregoing: assumptions it isl desiredl that:fuelshutolvalve:71be closed: (t1) under low speed operational?` pump 14. when and onlyjwhenthesproduced diiierential pressure fallsA `fromrthestated normal,v ofabontv 5 lbs. per square inch to a reduced. value. of 3 lbs; per square inch; and (b.) under high speedoperationopump 14; when the produced. dilerential':v pressure falls'. from a normal of about v lbs.. per square inch to ag reduced value of about 15. lbs; per square inch.

In order that'. differential pressure meter DP may transe latean indication of such reduction into an energization of fuel shutofffsolenoid72; that instrumentzis:providedwitli contacts 76 and 77 respectively engaged by pointer: 75 throughthe respectivepressure ranges of less than 3 lbs. per square inch and ofless than 1'5. lbs. pery square inch. These two instrument contacts 76 and.77 are. respectively connected with the backl and' front points of load. relay contact174` to achieve afunctioningnow to be described.

Assume first that the steam generator is operating at a loadingof less than 20% full rated andvcirculation pump 14is being driven at low speed (5001R. P. M.) by motor 34'. Under'this condi-tion load relay LR is released causing back contact 742 thereof to.` join the winding ofy solenoid 72 iwithlowrange vcontactfv 76 in instrument- DP; As long asfpump 14 creates ay dilferential" pressure higher than 3 lbs'. per'square inch pointer-75` is keptto the right of contacty 76, solenoid 72 is deenergized' and the fuel shutol valve-71' is allowed-to occupy its normally openposition'.

Should. now. the pump diierential pressure-r fall below 3 lbs.- per square inch, instrument DP, will movey pointer 75 to the left into engagement with contact. 76. This will energize shutoff valve 72 over a circuit extending from supply conductorSSthrough conductor 79.; engaged-.ele-

ments 75-76 of dlt'erential pressure meter DP, conductor 80, back contact 74 of released relay LR and the solenoid windingf72 tothe supply conductor- 56.

Thus energizedv solenoid 72`closes shutolvalve 71 and discontinues supplyof: fuel to thefbiirnei-ZSL Such discontinuancelowersthe=temperature in-combustion chamberY f 17 and thereby `protects the steam generatingtubesg12 fromdamage .due tol overheating;

Assume nextV that the steam generator is' operatingrin the load-range above-.20% ratedin-which circulation pump 14 is being driven at high speed (1500 R. P. M..) bv'turr' binef35'. Aslong-as-thezso driven pump createsa dilerential pressure ofl above 15 lbs.` per square; inch, instrumentv DP-f'holds pointerA 75 to the right'of contactf77. AsV earlier brought out, the-load'.` relay: LRI is picked upduring the assumedr high capacity-loading on the steam generatori, hence under lthe statedl condition `solenoid 7-2 isgdeenergized and-fuel' shutoff'valv-e 71`i's allowed to occupy-its normally open position.

Shoul'dnow the differentialv pressurefproduced by pump 14"fa-llfromv its normal of about 35 lbs. persquare inch to less than 15 lbs per square inch, instrument DP will move pointer 75 to`v the left into engagement with contact 77. This completes for shuto valve solenoid'72 an energizing` circuit that extends from supply conductor 55 through conductor 79, engaged elements 75'-77` of device DP, conductor 81; front contact 74 of picked up relay LR andthe windingnof'solenoid 72 to supply. conductor 76.

Thus energized solenoid`72 closes shutot valve 71 and by stopping further fuel supply to burner 25 lowers the temperature: in.. combustionchamber. 17 and,` thereby; safer guards the steam generating'tuhes-.12 from. overheating.

Application of control facilities to single motor pump drive'of Fig. 2-

In thesystem of Fig. 1 the low capacity pump driver took; the form ofL an electrical. motor 34 having` assumed: operatingspeed and rating valuesof 5,00 R. P. M". and: 15y horsepower, while. the high capacity pumpdriver took-the; form ofia steam turbine, 36 having ,assumed operating speed-f andrating' values of 1500 R. P. M. and, 100 horsepowerz. The novel. control and protective-facilities of. my invention'. which already have been described also are applicablefto situationsv wherein` the low speed'and the high speed drives for. the pump originate in a singleprime. mover insteadtions asa highcapacityv machine to drive pumpy 14- at,

about', 1500 R. P. M. 'fo-facilitate explanation it4 will further be assumed that during said low speedy opera.- tionthemotor 82 developsv about 15 horse power and duringthe high speed.l operation its rating is of the order.

yof 100 horsepower.

In the' arrangement of Fig. 2. connection ofA said low speedterminals withl power source Afv-B-C is. accom-- plished by the same. switchr contacts 42 and activating solenoid as were earlier describedfor Fig. l, and con.-

nection of motor 825 high speed terminals is'Y effected'X through normally open switch contacts. 41 which at proper times aieclosedtbya; solenoid 44 that correr sponds to device 44 of Fig; 1.

Comparing the diagram of Fig. 2 with that of Fig. 1 it will beseenf that inall other respects there.isaneiractL duplication; the 0nly=l changes, being the just described. substitution of two-speed motorV 82 for separate primes movers 34 and 36 and the attendant applicationof the.

controls respectively utilizedfor those separate-low speed and high Speed prime movers to the low speed and.y t0. the high speed windings of said motorV 82.

Accordingly; the-operation'of the Fig. 2 systemr exactly, duplicatest that already explained in detail for the: sys-l tem, of Fig.- l; the, only changes, beingl that the lowspeed facilities of motor 82l corneinto'operation in placeV of the single motor-34 of Fig. l and the high-,speed facilities ofmotorfSZ come intooperation in place of; the high; speed turbine. 36 of Fig; 1.

Because-.thefunctioning of the Fig. 2 system isV all? other; respects exactly the: same as the functioningof the. Fig. 1. systcm,.no'attempt.to repeat operation description is;4 herey deemed necessary;

Summary Ffrornthe foregoing; it' wil1 be seen that my invention-y has provided important improvements in the operation;y and protection; of,y forced circulation steam generators.

equipped with high-capacityl and. low-capacity driving.r`- means; forfthe .forced circulation pump; that one portion: of` said-f.V inventionresides inV improved means responsive to a measure of the steam load supplied by the generatori' for causingthe circulation pump to be driven at lowvspeed when' said' load 1s' lessthan a given value and at high speedwhenathe load exceedsY that value; thatsaidl facili- 3 tiesxetect" selection of;r the driving means and transfer:

from'. one. tothe other` automatically. and" ina simple.l yet highly reliable.- manner; and; that.I the invention further: Provides-l improved means' responsive to the: differential pressurescreated; by-the pump for protecting the. boiler parts; fromA overheating should said pumpV when driven at; either high speed orlow speedy fail to circulate water through the steamgeneratingtubesrat a rate that is ade-` quate for the'stearn load being carried bythe boiler.

Although I haveshown anA electrical system of con'-A trol and protection it will become apparent' thatthesarneresults can be achieved in other ways as through 'the medium ofcontrol facilities actuated either hydraulically or bytalrpressure;

The particularcontroland protective arrangementheretdisclosed is therefore. illustrative rather than' restctive-- and my inventive improvements accordingly have broad utility and are capable of wide application.

What I claim is:

1. In a steam boiler, the combination ofa combustion chamber, a burner for introducing into said chamber fuel that is to be burned therein, means for supplying said fuel to said burner at a rate adjustable to meet the steam load imposed upon the boiler, steam generating tubes associated with said chamber to receive heat liberated therein by a burning of said supplied fuel, a separating drum receiving from said tubes the steam which said heat generates therein and dischargingsaidreceived steam to the boiler load, a circulationpump connected to supply to and force through said tubes water taken from said drum, a low-capacity prime mover for driving said pump at a low speed, a high-capacity prime mover for driving said pump at a high speed, meansincluding a first instrument effectively responsive to the aforesaid steam load carried by said boiler for activating said low-speed pump driving prime mover when said load is less than a given value and for activating said high-speedv pump driving prime mover when saidvsteam load is greater than said given value, a normally-inactive shut-off device for the aforesaid burner fuel supply means, a second instrument responsive to the differential pressure across said circulation pump for indicating the rate at which that pump circulates water through said steam generating tubes, and means controlled jointly by said second instrument and by said first instrument for activating said fuel shut-off device in the event that said pump when driven by said low-capacity prime mover should fail to circulate water through said generating tubes at a predetermined low rate adequate to sustain steam loadings on the boiler which are below said given value and also in the event that said pump when driven by said high-capacity prime mover should fail to circulate water through the generating tubes at a predetermined higher rate adequate to sustain steam loadings on the boilerwhich are above said given value.

2. In a boiler of the type described having pump means for establishing a positive circulation through the steam generating tubes of the boiler the improvement comprising first prime mover means operatively associated with said pump means for driving the same at a predetermined high speed, second prime mover means operatively associated with said pump means for driving the same at a predetermined low speed, a control device effectively responsive to the steam load on the boiler and including means associated with each of said prime movers operative to activate the first and deactivate the second prime mover when said steam load exceeds a predetermined value and to activate the second and deactivate the rst prime mover when said steam load is less than v said predetermined value.

3. An organization as defined by claim 2 wherein the second prime mover comprises an electric motor.

4. An organization as defined by claim 3 wherein the rst prime mover comprises a steam turbine.

5. In a steam boiler, the combination of a combustion chamber, a burner for introducing into said chamber fuel that is to be burned therein, means for supplying said fuel to said burner at a rate adjustable to meet the steam load imposed upon the boiler, steam generating tubes associated with said chamber to receive heat liberated therein by a burning of said supplied fuel, a separating drum receiving from said tubes the steam which said heat generates therein and discharging said received steam to said steam load, a circulation pump connected to supply to and force through said tubes water taken from said drum, a low capacity prime mover for driving said pump at a low speed, a high capacity prime mover for driving said pump at a high speed, means effectively controlled by said steam load imposed on said boiler and operable to cause low speed drive of said pump by said low capacity prime mover when said load is less than a given value and high speed drive of the pump by said high capacity prime mover when the steam load exceeds said given value, a normally inactive shut-off device for the aforesaid burner fuel supply means, and means responsive to the rate at which said pump circulates water through said steam generating tubes for activating said fuel shut-off device in the event that said pump when driven by the said low capacity prime mover and when driven by said high capacity prime mover as aforesaid fails to circulate said water at a rate which is adequateifor the part'ic'ular'steam' load being carried byl the boiler.

6. In a steam boiler comprising a combustion chamber in whichfuel is burned, steam generating tubes vassociated with said chamber to receive heat from said burning fuel, a separating drum receiving from said tubes the steam which said heat generates therein and discharging said received steam to steam utilizing apparatus, and a circulation pump connected to supply to and force through said tubes water taken from said drum, the combination of a low capacity prime mover for driving said pump at a low speed, a high capacity prime mover for driving said pump at a high speed, an instrument actuated in response to the rate at which the aforementioned steam generated in said tubes is supplied to said steam utilizing apparatus and means governed by said instrument for activating said low speed pump driving prime mover and dcactivating said high speed pump -driving prime mover when the aforesaid rate is less than a given value and for activating said high speed pump driving prime mover and dcactivating' said low speed pump driving parme mover when said rate is greater than said given v ue.

7. In a steam boiler, the combination of a combustion y'ch-amber, a burner for introducing into said chamber fuel that is to be burned therein, means for supplying said fuel to said burner at a rate adjustable to meet the steam load imposed upon the boiler, steam generating tubes associated with said chamber to`receive heat liberated therein by a burning of said supplied fuel, a separating drum receiving from said tubes vthe steam which said heat generates therein and discharging said received steam to steam utilizing apparatus, a circulation pump connected to supply to and force through said tubes wateitaken from said drum, a low capacity prime mover for driving said pump at a low speed, an operation control device for said low capacity prime mover, a high-capacity prime mover for driving said pump at high speed, an operation control device for said high-capacity prime mover, an instrument responsive to the rate at which said steam generated in said tubes is supplied to said steam utilizing apparatus and means governed by said instrument for activating said low capacity prime mover control device and dcactivating said high capacity prime mover control device when the aforesaid steam rate is less than a given value and for activating said high-capacity prime mover control device and dcactivating said low capacity prime mover control device when said steam generating rate exceeds said given value.

8. In a steam boiler comprising a combustion chamber in which fuel is burned, steam generating tubes associated with said chamber to receive heat from said burning fuel, a separating drum receiving from said tubes the steam which said heat generates therein and discharging said received steam in accordance with the steam load on the boiler, and a circulation pump connected to supply to and force through said tubes water taken from said drum, the combination of a low capacity prime mover for driving said pump at a low speed, a high capacity prime mover for driving said pump at a high speed, a steam flow meter responsive to the rate at which the steam, generated in said tubes as aforesaid, is taken from said drum to supply the aforesaid load, and means governed by said steam ow meter for activating said low capacity and dcactivating said high capacity pump driving prime mover when the aforesaid steam flow rate is less than a given value and for activating said high capacity and dcactivating said low capacity pump driving prime mover when said steam flow rate is greater than said given value.

9. In a steam boiler comprising a combustion chamber that is provided with a burner, means for supplying fuelto said burner and for adjusting the flow rate of said fuel to meet the steam load imposed upon the boiler, steam generating tubes associated with said chamber to receive heat liberated therein by a burning of said supplied fuel, a separating drum receiving from said tubes the steam which said heat generates therein and discharging said received steam to said boiler load, and a circulation pump connected to supply to and force through said tubes water taken from said drum, the combination of a low capacity prime mover for driving said pump ata low speed, a high capacity prime mover for driving said pump at a high speed, a fuel ow meter responsive to the rate at which the aforesaid fuel is supplied to said burner, `tor;4 ther-purpose. off generating steam in; saidA tubes... and means governed by said fuel ow meter for actwatlng" saidilowv speed; and. deactivating, said!` high, speed.v pump driving. prime.y mover; whenl the; aforesaid-1` fuel supply rate. is.v less than a. given 4val-ue and foractivating` said High. speed and1deactivating said: low speed pump. driving; prime mover when. said; fuel supply rate is greater than said' given*l value.,

. 110. In afvsteam holler comprising ya. combustionv cham herr, aburner for introducing, into said chamber fuel.

that is to be burned; thereim. means,y fon supplying` said fuel. tor said. burner. atV arate, adjustable. to meet the steam loadt imposed upon7 the'zboiler, anormally inactiveshut oi devicefor said.fuel..supplysteam generating tubes as sociated.V with vvsaid. chamber. to.- receive; heat; liberated` therein. by a burning of said supplied fuel,` a. separating 5 dwmleceiving from saidtubes the steamrwhich saidheat generates. therein` and discharging the received; steam.

t.said load, anda circulation-pump connectedtu` supply to. and force through said tubesf water taken from saidv drum, the. combination. of' a. low. capacity prime: mover fbrf driving said. pump at a low speed when` thesteam loadV supplied by said boiler is less than a given valuea highecapacity, primermover. for. driving said pump atta speed.l when said'. boiler steam load.` is greater than.`

fails to maintain, sa-id water circulation above a. prede?.

termined', low rate adequate for steam loadings.. on; the, boilerl which are-.less than theaforesaid givenvalue.4 and. alsoin the event thatf said pump when driven byy said high speed prime, moverfails. to maintain said waten circulation, abovel a` predetermined higher rate adequate: for. boiler loadings which aregreater.` than said given: value;

I References Cited. in the file of.. this patent 'UNITI-E13 STATES PATENTS' 1,696,892

French et al. Dlec. 25, 19.28 1,859,857y Whittamy May2z4, 1932i 1,988,643 Anderson, Jr. Jan; 22;l 1935 2,201,161.18 La Mont Mayy 21,.y 19401 2,320,503. l Badenhausen lune I, 1943 2,402573l- Effi-isch' Aug'- 13,1946' 

